Useful Volatile Organic Biomarkers for Discriminating Spoilt Onion Cultivars in Sokoto

Abstract

Microorganisms degrade food components in order to access nutrient available in such food and in return produce organic compounds from the breakdown of the food components. These organic compounds hold potential to be exploited as biomarkers to detect the presence of such microorganisms. This study was conducted to evaluate fungi associated with volatile organic compounds production in spoilt onion cultivars. A total of 54 onion bulbs which include 45 healthy and 9 spoilt onion bulbs belonging to three cultivars were used for this study. All laboratory investigations were carried out by standard methods. Four fungal genera were identified and these include Aspergillus, Fusarium, Mucor and Candida. The GC-MS analysis revealed the presence of twenty six (26) volatile compounds in spoilt white onion bulb, (9) in yellowish-brown and (8) in the purple variety, respectively. White onion bulb had the following dominant compound; nonane (11.97%), decane (11.96%), octane (9.3%) of which ten was unknown. The compounds sulphurous acid, 2-ethylhexylisohexyl ester (18.60%), phenol 2,6-bis(1,1-dimethylethyl)-4-methyl (7.90%) were dominant in yellowish-brown cultivar including five (5) unknown, while the predominant compounds in the spoilt purple onion variety were, phthalic acid, di-(1-hexen-5-yl)ester (69.64%) and phenol-2,6-bis (1,1-dimethylethyl)-4-methyl, of which five were unknown. This study suggests that these unique volatile organic compounds could provide the bedrock for restraining postharvest losses and the volatile organic compounds could also form baseline knowledge for discriminating diseases associated with onion.